Re: [PATCH 2/2] virtio: Drop out of coroutine context in virtio_load()

[Stefan Hajnoczi]

On Fri, Sep 08, 2023 at 10:59:48AM +0200, Kevin Wolf wrote:
> Am 07.09.2023 um 20:40 hat Stefan Hajnoczi geschrieben:
> > On Tue, Sep 05, 2023 at 04:50:02PM +0200, Kevin Wolf wrote:
> > > virtio_load() as a whole should run in coroutine context because it
> > > reads from the migration stream and we don't want this to block.
> > 
> > Is that "should" a "must" or a "can"?
> > 
> > If it's a "must" then virtio_load() needs assert(qemu_in_coroutine()).
> > 
> > But the previous patch mentioned that loadvm for snapshots calls it
> > outside coroutine context. So maybe it's a "can"?
> 
> Where this makes a difference is when the function indirectly calls into
> QIOChannel. When called from a coroutine, it yields while waiting for
> I/O, and outside of a coroutine it blocks. Yielding is always
> preferable, but in cases like HMP savevm/loadvm we also don't really
> care because it's synchronous anyway.
> 
> Whether that makes it a MAY or a SHOULD in the RFC sense, you decide.
> If you wanted to make it a MUST, you'd need to check all callers first
> and change some of them.

Thanks for clarifying. It is "can".

Stefan

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